Darpa's XS-1 Experimental Spaceplane

​The US Military high tech research agency, DARPA (the Defense Advanced Research Projects Agency), is working to develop a reusable spaceplane that would replace the traditional, expendable, first stage of a multi-stage launch vehicle.

Artist's concept of the XS-1 Experimental Spaceplane being designed by Northrop Grumman, with help from Scaled Composites and Virgin Galactic, for DARPA.
Credit: Northrop Grumman

The idea is to construct a hypersonic spaceplane that would replace the first stage, launch a small payload or upper stage booster into orbit, then fly back to the launch site -- and turn around and do it again within 24 hours.

The initial payload capacity would be small, but quite cheap. DARPA envisions payloads on the order of 3,000 to 5,000 pounds (1,360 to 2,267 kilograms) at a cost of only $5 million.

The key technology driver, though, is to develop an "aircraft-like" operability by flying the XS-1 Experimental Spaceplane, which should reach speeds in excess of Mach 10, ten times in ten days. ​

The XS-1 Experimental Spaceplane is just the newest take on a decades long program to develop reusable aircraft that can reach the edge of space.

First, there was the X-15 program, which ran during the 1950's and '60's.

Then there was the Rockwell X-30 -- an advanced technology demonstrator for the National Aerospace Plane (NASP) program in the 1980s that was cancelled in the early '90s before a prototype was completed.

More recently, Reaction Engines LTD in the UK has been working on Skylon - a fully reusable spaceplane that has engines that can can operate as either a jet engine or rocket engine.

Credit: Reaction Englines LTD

But, although spaceplanes have been developed as the upper stage component of a launch stack​, no one has actually developed a working version of a first stage vehicle.

DARPA originally announced the program in 2013 which is now in Phase 1. In 2014, three teams were selected to compete for the actual flight contract:

In August 2015, the contractors received additional funding to continue their XS-1 design concepts for a Phase 1B activity.

DARPA began Phase 2 on April 7, 2016. In this phase, the agency plans to narrow the competition down to just one company. A test flight is expected in 2018, with an initial orbital mission as early as 2020.